Oscillating piston apparatus

ABSTRACT

A substantially closed cylinder containing a compressible fluid, such as air, and a free piston for reciprocation within the cylinder, and a number of elongated passageways, each having an end opening into the cylinder and an opposite closed end. The passageways are heated along their lengths. The fin-shaped open end portions and the cylinder wall are cooled. Piston reciprocation is effected by the force of heated expanding gas moving from the closed ends of the passageways to drive the piston in one direction as the gas cools in the region between the piston end and the cooled open ends of the passageways. The piston compresses the gas at the opposite piston face, which gas in turn drives the piston back after the force of the compressed gas exceeds the force of the cooling gas to regularly repeat such cycle.

United States Patent Schuman l *Aug. 19, 1975 l l OSCILLATING PISTONAPPARATUS Primary LAumirzcr-Williz1m L. Freeh [76] wanton Mark schumanml G St SW Assistant Examiner-Gr P. LaPointe APL N0 516 Washington DCArmrney Agent, or Firm-Lowe King & Price 20024 [*1 Notice: The portionof the term ofthis patent l57l ABSTRACT Subsequent to Apr. 30 I99! hasbean A substantially closed cylinder containing a compress- Caimed. ihlefluid such as an, and a free piston for reciproca' tion within thecylinder, and a number of elongated [23 il Apt 29 1974 passageways eachhaving an end opening into the cylinder and an opposite closed end Thepassageways lzll Appl' 465'l38 are heated along their lengths. Thetin-shaped open Related 5 A fi fl Data end portions and the cylinderwall are cooled. Piston [63] Continuation of Ser No. 227.514, Feb, [8.1972. f is effected by force of heated Pat No. 1807904 which is ucontinuation-impart of pandmg gas f 9 h Clnsq encls of the set NO ]2|37| March 97L uhundune sagewnys to drive the pIston in one direction asthe gas cools in the region between the piston end and the [52] Us. CL H60/5; 417/207; 60/520 cooled open ends of the passageways. The pistoncom 5 Int 1 H F03 7 0 presses the gas ill the opposite piston face.which gas 53 Fie|d f Search H 0 24 417 307 in turn drives the pistonhack after the force of the compressed gas exceeds the force of thecooling gas to {56] References Cited regularly repeat such cycle.

UNITED STATES PATENTS 88 Claims. 18 Drawing Figures 3.807904 4/l974Schumun 4. 417/207 OSCILLATING PISTON APPARATUS RELATIONSHIP TOCO-PENDING APPLICATION The present application is a continuation of mycopending application. Ser. No. 227.514. filed Feb. 18. [972 for"Oscillating Piston Apparatus". now U.S. Pat. No. 3,807.904, grantedApr. 30. I974. which in turn is a continuation-in-part of applicationScr. No. l2l.37 l filed Mar. 5. 197], now abandoned.

BACKGROUND OF THE INVENTION The apparatus herein relates to anoscillating piston and cylinder construction which may be used as apump. such as is described in my U.S. Pat. No. 3.489.335, now reissuedas U.S. Pat. No. Re. 27,740 or as a gas analyzer mechanism such as isdisclosed in my U.S. Pat No. 3.516.745. or as part of an engine such asis described in US Pat. No. 3.583.l55. or other devices which utilizethermal energy for power. The apparatus herein is a simplification ofandin some directions an improvement of the equipment described in theforegoing patents and applications.

More specifically. the present invention provides more preferred formsof heat transfer surfaces for driving a moving part. e.g., a piston.whereby the heat transfer surfaces are in structures that are relativelyefficient and compact. Means are also provided for eliminating some orall of the valves and other pieces of mechanism which were utilized inthe abovementioncd equipment for restricting fluid flow into a heatingchamber and for positioning the center or piston oscillation.

SUMMARY OF THE INVENTION Summarizing. the invention herein contemplatesforming a number of elongated passageways. each opening into a drivechamber near one face of a moving oscillating wall of the chamber. whichmay be formed by a piston face. Each of the passageways is heated andthe drive chamber is cooled whereby a temperature gradient existsbetween the drive chamber and the passageways. A compressible fluid.such as air. is forced by the piston face into and through thepassageways. The fluid is heated in the passageways and is returned backto the drive chamber to drive the piston in one direction.Simultaneously, the piston compresses the fluid at its opposite face andthe compression offluid in this opposite chamber of the cylinder inwhich the piston oscillates causes the piston to rebound or return.Fluid entering the drive chanber during the oscillation cycle issimultaneously cooled to assist in driving the piston in the otherdirection to thereby regularly repeat the cycle of piston and gasmovement.

By using long passageways. heated near one end and cooled near theiropenings into the drive chamber for providing a difference intemperature between the passageways and the drive chamber.thermopneumatic energy is thereby provided to sustain the natural resonance of oscillation of the piston between the gaseous compressionsprings at opposite faces of the piston. without the need for additionalvalving and other mechanical controls. A sealing action of the pistonagainst side walls of the cylinders separates the gaseous com pressionsprings and the mass of the piston decreases the resonant frequency toimprove the efficiency and power of the device.

These and other objects and advantages of this invention will becomeapparent upon reading the following description. of which the attacheddrawings form a part.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic. elevational.cross-sectional view of the oscillating piston apparatus;

FIG. 2 is a cross-sectional view taken in the direction of arrows 22 ofFIG. I;

FIG. 3 is a top plan view of the piston taken in the direction of arrows3-3 of FIG. 1;

FIGS. 4-11. inclusive. show successive positions of the piston duringone cycle;

FIG. 12 is an elevational. schematic, crosssectional view of amodification;

FIGs. l3l7 each illustrate schematic, sectional. views of differentmodifications; and

FIG. I8 is a cross-sectional view of a novelty device utilizing theprinciples of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIGS. I-3. theoscillating piston appara tus I0 is formed of a closed cylinder IIcontaining a free piston I2. The piston has an upper drive face I3formed with integral. wedge-shaped tins 14. The opposite piston face 15forms a compression face. Free piston 12 can be considered as having anintegral form that has substantially the same cross sectional dimensionsand working area throughout its length.

The piston I2 divides the cylinder into an upper, drive. cooling chamberportion 16 and a lower. compression chamber portion I7 which arenormally separated from each other by a seal formed between the sidewalls of cylinder II and piston I2. The upper and lower faces of piston12 can be considered as moving walls of variable volume chambers havingfixed walls defined by the upper and lower portions of cylinder 1 l.

The upper end or head 18 of the cylinder located above the upperchamber. is formed with a passageway means comprising a number of heatedpassageways 19. having closed upper ends and lower ends 20 which openinto the upper chamber I6 with flared or outwardly wedgeshaped openingsto provide greater surface area for cooling. The lower ends 20correspond in shape to the wedge-shaped fins 14 on the piston 12. toform mating variable geometry cooling passageways. Alternatively. theupper drive face 13 of the piston may CI'OSS- be flat and the lower ends20 of the passageways I) not' flared or wedge-shaped. The passagewaylower ends 20 variably exposed by the fins 14 of piston I2 serve aspassageway means for cooling heated gas flowing into drive chamber I6.

The upper or closed ends of the passageways I9 are heated by means of asuitable. independent heating mechanism. such as heating tube 2] forcarrying a heated lluid through exterior pipes 22 from a suitableexternal heater 23. The heating mechanism may be varied and its specificconstruction forms no part ofthe invention herein A lower heating tubeZla may also be included to supply heat some distance below the upperends of the passageways.

The lower ends portions or open ends 20 of passageways I) are cooled bycooling tube 24. connected by exterior pipes 25 to an external coolingdevice 26. Another cooling tube 2.4a. at the bottom of the flared ends20. may also be include for better cooling. Also a third cooling tube24/), arranged in the cylinder wall, may be used to cool the cylinderwall surface in the re gion traversed and variably exposed by the upperdrive face I3 of the piston. The form of the cooling device is not partof the invention and may be varied. The object here is to provide one ormore heated passageways opening into a cooled chamber containing thepiston face. such that the drive chamber has one or more vari ablyexposed cooled passageways. The cooled and heated passageways are formedof a heat conductive material so that there is a temperature variationbetween the heated passageways and the cooled drive chamber includingthe cooled passageway openings. Preferably an insulating layer 27 isprovided between the wall portions defining upper and lower parts of thepassageways to reduce wasteful heat flow. More than one insulating layermay also be used. forming a somewhat laminated structure. Instead ofbeing straight and arranged in parallel. the fins and passageways may bearranged in other configurations, e.g.. the passageways and fins may becircular and arranged in concentric rings. The passageways may. in thealternative, be outside of the cylinder and enter the drive chamber viaa port in the side wall of the cylinder.

The upper chamber 16 is connected to the lower cylinder chamber 17,around the piston. by a shunt pipe 28 containing an upper, normallyclosed valve 29 and a lower. normally closed valve 30, in turn connectedto a gas or air inlet 3].

Valves 29 and 30 are made of a conventional wager. ball, or similar typeof pressure closing valve. of the type which is essentially sealed whenclosed. However. the valves are generally formed so that they do nottightly close at relatively low pressure differential but permit someleakage through them. Leakage through valves 29 and 30 decreasessubstantially to zero as the differential pressure across each valveincreases.

The valves 29 and 30 permit a small upward flow of gas around thepiston. When the piston moves up. some gas may leak through the valve topipe 31. When piston 12 is near the top of its stroke. a small amount ofgas enters into the lower chamber I7 due to the valve opening. On thepiston downstroke, valve 30 closes whereas gas may enter through valve29. Due to the weight of the piston. there is a little less gas. and alittle higher compression ratio. below the piston than above it. Thus,gas tends to flow upwardly around the piston. and is replaced by a netintake of gas through valve 30 and a net leakage through valve 29. Ifpiston 12 drifts too low. the higher compression ratio below its lowerface causes upward movement of the piston, whereby more gas is drawnthrough valve 30.

To start the reciprocation or oscillation of piston 12, a startingmechanism is necessary. This is schematically illustrated as starter 32.including an external cylinder 33 connected by a pipe 34 into the lowerchamber I7 of the main cylinder I]. A piston 35 connected to a pistonrod 36, which is moved back and forth (left to right and vice versa asillustrated) by a suitable drive mechanism (not shown to draw gasthrough valve 30 into the cylinder 33 and to move gas from the cylinder33 into the chamber I7 and vice versa to force the piston 12 to move upand down. Once the piston 12 begins moving due to the full operation ofthe heating device 23 and cooling device 26. the starter is deactivatedand positioned close to chamber I7. i e., at the extreme left.

as viewed in FIG. I. Usually a single cycle of the piston 35 issufficient to initiate oscillation.

The oscillation of piston 12 at a particular frequency is determined bya number of factors, including: the inertia or mass of piston 12 and theeffect of pneumatic springs formed by the gases compressed by the upperand lower faces of piston 12 while the piston is oscillating. The meansfor sustaining oscillation includes these factors and further includes:the thermal lag properties of the passageways means, i.e., the time orportion of an oscillating cycle of piston I2 for the maximum and minimumgas temperatures to occur after maximum and minimum compression of thegas in the chamber formed by the passageways and the upper face ofpiston 12'. the amount of heating of gas in passageways 19; the amountof gas cooling in drive chamber 16. It is to be noted that the net flowof cool fluid (fluid colder than the temperature of the hot walls of thepassageways 19) that flows or is induced to flow into passageways 19, bythe upper face of piston 12, while the piston is approaching thepassageways, is primarily and directly responsive to pressure variationsin this fluid. Further, the pressure variations in the fluid beingcompressed into passageways I9 is primarily and directly responsive tothe changes in the volume of the chamber defined by the upper face ofpiston 12 and the passageways l9, which changes in volume are caused bythe moving chamber wall comprised of the upper face of piston 12.

OPERATION FIGS. 4-l I, inclusive, show successive steps in one cycle ofmovement of the piston 12. Starting with FIG. 4, the piston is shown inits bottom, dead center postion. At bottom dead center, the gas belowthe piston in the compression chamber (see arrows pushes the pistonupwardly with greater force than is exerted against the upper face ofthe piston by the expanded. cooling gas in the drive chamber.

FIG. 5 shows the piston moving upwardly under the rebound of thecompressed gas in the compression chamber and driving the still coolinggas upwardly into the passageways 19.

FIG. 6 shows the piston in the top dead center position, wherein thepressure of the gas below piston I2 is less than the pressure of the gasabove the piston and the gas above the piston is being heated andbeginning to return downwardly from the upper closed ends of thepassageways 19.

FIG. 7 shows the gas. while still being heated in the passageways l9expanding from the passageways into the upper. drive chamber to forcepiston 12 downwardly with the piston compressing the gas below it.

In FIG. 8, piston I2 is about one-quarter of the way down, compressingthe gas below it to force the gas downwardly in response to theexpanding gas above the piston. The expanding gas above the piston 12 issimultaneously being cooled at the lower or outlet ends of passagewaysI9.

In FIG. 9, piston 12 is about one-half way down, and the force of thegas being compressed beneath the piston is increasing while the force ofthe gas above the piston is decreasing due to the increased volume ofthe drive chamber and the decreased volume in the lower chamber. as wellas the cooling of the gas in the drive chamber.

FIG. I0 shows the piston about three-quarters of the way down with thepressure of the compressed gas below the piston now exceeding thepressure of the cooling gas above the piston so that the speed of thepiston decreases.

FIG. 11 shows piston I2 at its bottom position again. with thecompressed gas below the piston now pushing the piston upwardly againstthe decreased pressure of the cooling gas above the piston; at this timethe pressure above piston 12 is considerably less than the pressurebelow the piston. Thereafter. the cycle repeats with the pistor. rapidlyoscillating or reciprocating up and down during the repetition of eachcycle.

MODIFICATION FIG. I2

FIG. 12 shows a modification wherein the cylinder head 18a is arrangedto one side of the top of cylinder I la and opens into the top ofcylinder through a nozzle like opening 40. The piston 12a may have asmooth or flat top. The fins may be omitted whenever significant poweror amplitude of oscillation is not required. The cylinder wall is cooledby cooling tube 241). The operation and construction is otherwise thesame as that described above in connection with FIG. I. By locating thepassageways 19:: off to one side of the cylinder. at single set ofpassageways can be used to synchronously drive more than one piston (seeFIG. 14, below). Also,

without the fins, the cylinder is clear for use as a variable volumeoptical chamber gas analyzer by providing the necessary transparentwindows in the cylinder either above or below the piston as is describedin my prior U.S. Pat. No. 3,516,745, of June 9, I970.

MODIFICATION FIG. I3

FIG. 13 shows a construction having a pair of side cylinder heads 18/),181', each having heating tubes 2I and 2112. as described above. Thecylinder heads open through nozzle-like openings 41. into the cylinderllh, above and below the piston 12/). The piston has upper and lowerfins 42 which mesh with fixed cooling fins 43 having cooling pipes 24.Thus, the piston I2his positively driven in both directions so that theopposite faces of the piston can be considered as opposed moving wallsofa pair of chambers, which walls have a relative phase displacement of180.

FIG. 13 also shows check valves 29 and 30 polarized to pass air throughthe chambers above and below piston 12b for positioning the center ofpiston oscillation. Adjustable. spring biased, flow limiter valve 29apasses an adjustable amount of air to a load (not shown) only when thepressure in the upper cylinder chamber is greater than load pressure bya small amount determined by the position of spring 291'. Check valve29!) keeps air from returning from the load. Check valves 29a and 29hcan control the pumping power supplied to a load so that piston [2/2 isnot stalled.

MODIFICATION FIG. 14

FIG. 14 shows another modification wherein the cylinder head 18d. whichhas the same configuration as those shown in FIGS. I2 and 13, has afluid flow path into the center of the cylinder 110 through nozzle-likeopening 45. A pair of pistons 12c. 12d, each having fins 46 on theirinner faces. mesh with spaced apart central cooling fins 4748, havingintegral cooling pipes 24d. The two pistons are synchronized to move inopposite directions at all times. That is. pistons [20 and 1211 aredriven apart by the cooling gas located between them, and reboundtowards each other by the gas which they compress at the opposite endsof the cylinder. Synchronizing oscillation of the two pistons in thismanner can essentially eliminate vibration ofthe device. More than twopistons can also be synchronized in this manner. Also an additional setof cooling fins in. and heated passageways opening into. eachcompression chamber, can be added for additional power. The facing facesof pistons [20 and 12d can thereby be considered as synchronized movingwalls of a variable volume chamber. The chamber walls move toward eachother to compress gas fed into passageways of cylinder head 18:! andmove away from each other to expand the chamber volume in response toheated gas being ejected from the passageways.

MODIFICATION FIG. I5

FIG. I5 illustrated a modification which is similar to that shown inFIG. 1 above. except that an additional piston 120 is added at the upperend and passageways I9 are not closed at one end. Thus, the cylinder lidis elongated upwardly. as are the passageways I9. The cooling tubes 24and 24a and the heating tubes 2| and 210 are duplicated and a secondinsulating or thermal barrier 27a is provided. The upper piston 120 isprovided with fins as in FIG. I. to mesh with the flared upper ends ofthe passageways 19. The operation is the same as that described above inconnection with FIG. 1, except for the driving of two pistons 1242a,instead on the one piston as illustrated in connection with FIG. I.Alternatively. the stationary and moving fins may be omitted but thedrive chamber walls would nevertheless be cooled. Gases flowing in theupper and lower portions of passageways I9 in response to oscillation ofpistons I2 and I20 have a tendency to remain separate from each othereven though there is no mechanical obstruction across the passageways.

MODIFICATION FIG. 16

FIG. 16 illustrates an oscillating piston apparatus 50 including acylinder which contains a single piston 12f. having lower face finsmeshing with fixed cooling fins 5l. Fins SI include cooling tubes 52similar to those described above in connection with FIGS. I3 and 14. InFIG. 16, head [8a, which is the same as the heads described above inconnection with FIGS. 12, I3 and I4, is offset to one side and opensinto the cylinder on the side of the cooling fins SI opposite the piston12f.

For purposes of positioning the piston 12f. without using valves,vertical grooves 53 are formed in the center portion of the cylinder II0. that is in the wall of the cylinder. Grooves 53 are by-passpassageways around a portion of the cylinder, which passageways have afluid flow impedance that is substantially the same to fluid flow inboth directions through the passageways. Thus, as the piston moves upand down, the leakage of gas, above and below the piston through thegrooves 53, tend to maintain center of piston oscillation near thecenter of grooves 53. If, for example, the center of piston oscillationdrifts below the center of the grooves 53, more gas leaks downwardlyaround piston 12f through the grooves 53 while the piston is in theupper portion of its stroke, than leaks upwardly during the bottomportion of its stroke. There is, thereby, a net flow of gas downwardlyto raise the center of piston oscillation upwardly.

MODIFICATION FIG. 17

FIG. 17 illustrates apparatus 60 which is identical to that describedabove in connection with FIG. 16, except that instead of the centeringgrooves. Ushaped by-pass tubes 61 are formed in the wall of the cylinderfor purposes of keeping the center of piston oscillation near or at thecenter or midpoint of the U-shpaed bypass tube 61. In FIGS. 13. I4. 16and I7 the heated passageways may alternatively be connected to thedrive chamber(s) via a port(s) in the cylinder side wall be tween thepiston and the fixed cooling fins.

MODIFICATION FIG. I8

Reference is now made ot FIG. 18 wherein there is illustrated a noveltydevice or a physics demonstration device adapted to be powered by heatfrom a conve nient source. such as a lamp of the incandescent type. Apair of arcuate. heated passageways. 71 is located in a partiallytransparent housing 72 having a shaped adapted to mate with anincandescent light bulb globe (not shown). The globe supports housing 72with the aid of metal clip or holding strap 73 that is fixedly mountedon housing 72 and is adapted to be frictionally connected to the globe.Heating of passageways 71 by heat from the lamp can be augmented byproviding the housing 72 with radiation absorbing substances. e.g..colored glass. It is to be understood that a single heated passagewaymay provide sufficient heating to operate the device.

Passageways 71. as well as passageways 19, are rcla' tively long andhave considerable breadth. but are relatively narrow in width to provideoptimum oscillation of gases therein. If housing 72 and passageways 71are formed ofa relatively weak material, e.g., glass, spacing betweenwalls of the passageways is preferably maintained by spacers 74, thatare sufficiently small to have only a slight effect on fluid flow in thepassageways.

One end of each of passageways 71 is connected in fluid flowrelationship to one end of hollow tube 75, that is downwardly dependingfrom housing 72. The other end of tube 75 is connected in fluid flowrelationship with transparent cylinder 76 that contains free piston 77.Cylinder 76 can be maintained securely in situ by spring clip 80 that isadapted to be secured to a suitable support. such as a lamp pole thatcarries the bulb for supporting housing 72. Gas in cylinder 76 is cooledby air from the surrounding environment, without resort to cooling bycooling coils. To center piston 77. cylinder 76 includes a number oflongitudinal grooves 78. centrally located on its interior side wall.

To initiate oscillation of piston 77. the lower end of cylinder 76 is influid flow relationship with starter 78 that includes a rubber orplastic bellows 78 having an upper interior wall bonded to the exterior.lower wall of cylinder 76. Leaf springs XI catch the folds or lower endface of bellows 79 to maintain the bellows in a compressed state afterthe bellows has been con1- pressed by an operator. Prior to compressionofthc bcl lows the lowcr face of piston 77 bciirs against the up permostfold ol'bcllows 79. In certain instances. it is dc sir-able to space theuppermost bellows lold from the lower edge of cylinder 76 to provide aleaky cylinder during starting. whereby air can get below the lower edgeof cylinder 76 and establish a better rebound chamber.

l tl

In each of the described embodiments, by using the ideal gas law it canbe shown that for a given low compression ratio (less than 2:1 thepneumatic power supplied by the heating and cooling means to the pistonto sustain piston oscillation is approximately proportional to theamplitude or amount of temperature variation of the gas during the cycleand to the sine of the phase angle of thermal lag introduced primarilyby the passageways, i.e.. the phase leg of the variation in the averagetemperature of gas in the chamber with respect to the instantaneouscompression ratio. The instantaneous compression ratio can be defined asthe ratio of the maximum chamber volume to the instantaneous chambervolume. As illustrated, the length and breadth of each passagewaytypically are each substantially greater than the passageway width.which may be substantially constant throughout the length and breadth ofthe passageways. The passageway width is chosen according to the desiredfrequency of piston operation to be sufficiently narrow and uniform toheat or cool substantially all of the gas in the passageway sufficientlyto provide an adequate amplitude of temperature variation. Heating isprovided by passageways I9 and cooling by passageways between teeth 14of piston 12 and by the cylinder wall portion traversed by the pis tonface.

The amplitude of the variation in average gas temperature during thecycle is determined by the amount of gas which is heated and cooledduring the cycle and also by the amount of heating and cooling of thisgas.

The passageways are preferably sufficiently narrow to allow heating orcooling of the gas emerging from the passageways throughout thesubstantially all of the CI'OSS section of the passageways. wherebythere is heat ing or cooling of gas near the center of the passageways.as well as at the walls of the passageways. The passageway width must.however. be wide enough to readily admit sufficient quantities of gasfor heating or cooling of the gas in the passageways 19. The passage waywidth must also be wide enough to provide an adequate angle of thermallag such that gas is being heated and fed from the thermal lag heater tothe piston as the piston is moving away from the heated passageway, andgas is being cooled in the thermal lag cooling chamber (drive chamber)as the piston moves toward the heated passageways. to maintain thepiston in oscillation. Thus. a compromise width is generally chosen atany given frequency of operation to maximize the product of theamplitude of the temperature variation and the sine of the thermal lagangle. so as to increase power and efficiency. Because ofthe thermal lagrequirement. a heat exchanger of this invention typically has apassageway width greater than that of heat exchangers employed inStirling cycle engines operating at the same frequency.

The breadth and length ofa passageway are generally each made largerthan the width in order to increase thc \olumc and decrease the lluiddrag of the passage- .i I hereby. thc amount of gas that can be heatedor cooled by the passageway is incrcascd. with :1 minimum increase insurface arca and viscous drag. The resulting passageway structure isrelatively compact and pro vides good heating and cooling paths throughthe solid material forming the passageway walls. Ihcrcby c\tcr nalheating and cooling of the passageways is made more cllicicnt.

The passageways thus have a characteristic thermal time constant forheating or cooling fluid. The time constant is primarily determined bythe average width of the passageways, and secondarily by other factorssuch as length, and breadth, smoothness. properties of the fluid, andconditions of operation. These factors are chosen according to thedesired frequency of operation to provide a thermal time constant whichresults in a sufficient phase angle of thermal lag at the oscillationfrequency to sustain oscillation and to provide an adequate or optimumamplitude of oscillation. The proportionality mentioned above forcompression ratios less than 2:l may be less accurate for highercompression ratios but is nevertheless valuable as a guide fordesigning. at a given frequency of operation. an optimum thermal lagheating chamber and an optimum thermal lag cooling chamber.

Because of the thermal lag requirement. it is desired that heating ofgas predominate over cooling for a period of time after maximumcompression. Correspondingly. it is desired that the net cooling of gasnear minimum compression continue for a period of time after minimumcompression.

It should be understood that almost any compressible fluid. such as aliquid and its vapor. may be used as the working fluid of this device.However. the thermal lag device of this invention. by itself. is notexpected to be as efficient an energy converter as some existing heatengines.

It should also be understood that the center of oscillation of all thepistons illustrated in all the embodi ments herein can be positionedeither by check valves. similar to the techniques shown in FIGS. I and13, or by passageway means bypassing a portion of the cylinder wall. asillustrated in FIGS. 16, I7 and 18. For example, in each of FIGS. I4 and15, the pistons could be positioned by means of three inlet check valvesor by means of two by-pass passageways or grooves. In addition. thecheck valve arrangement illustrated in FIG. 13 for pumping gas can beadapted to any of the embodiments illustrated herein. Pumping power canthus be drawn from any and all chambers of the devices illustrated byappropriately connecting the check valves to the chambers.

While there have been described and illustrated several specificembodiments of the invention, it will be clear that variations in thedetails of the embodiments specifically illustrated and described may bemade without departing from the true spirit and scope of the inventionas defined in the appended claims. For example. the passageways meanscan modify the thermal lag and the amount of heating of the gas byforming the passageway wall material to have a specific heat, thermalconductivity and geometrical configuration to provide a thermal timeconstant that causes cycling of the wall temperature at substantiallythe same frequency as the piston oscillates.

The device of FIG. 18 can be modified in numerous ways, such asproviding an upwardly extending hollow tube to connect the heatedpassageways with the cylinder containing the free piston. It is alsopossible to elim inate clip 73 by forming the passageways in a pair ofin terconnected sections, each adapted to fit on opposite sides of alamp globe and dimensioned to be slighly smaller than the globe so as tobe frictionally held on the globe with the aid of a fluid conduitconnecting the two sections together.

The device described herein may also be used as a cooling device, e.g.,for cooling a typical engine valve. Thus. the valve head would containthe heated passageways and the cooled valve stem would contain theoscillating piston. Oscillation of the piston and a gas or fluid withinthe sealed valve would cool the valve head and valve seat bytransferring heat to the valve stem and valve guide and thence to awater jacket or other conventional means for cooling a valve stem.

What is claimed is:

I. An oscillating piston apparatus comprising a cylinder. a free pistonin the cylinder. said cyliner having a side wall with a port therein, arebound chamber containing compressible fluid for reversing the motionof the piston. said rebound chamber having as a moving wall portion aface of the piston, means including said rebound chamber for sustainingoscillatory motion of the piston in the cylinder and means forcontrolling the location of the center of oscillation of the piston inthe cylinder. said controlling means including said rebound chamber anda passageway communicating with the cylinder via the port. saidpassageway by-passing a portion. and only a portion of the axial lengthof the cylinder. said passageway having a fluid flow impedance which issubstantially the same for fluid flow in either direction through thepassageway. wherein said port. said by-passecl portion of the cylinder.and an unbypassed portion of the cylinder are all at least partiallytraversed by the piston.

2. The apparatus of claim I wherein the free piston is of substantiallyintegral construction.

3. The apparatus of claim I wherein the crosssectional dimensions of thefree piston are substantially the same throughout substantially all ofits length.

4. The apparatus of claim wherein the means for sustaining includesmeans for alternately heating and cooling the fluid.

5. The apparatus of claim I wherein the means for sustaining includesheated passageway means communicating with said cylinder.

6. The apparatus of claim 5 further including means for heating saidheated passageway means.

7. The apparatus of claim 5 wherein said heated passageway meansincludes at least one passageway having a characteristic length andbreadth which are each substantially greater than its characteristicwidth.

8. The apparatus of claim I further including another rebound chamberfor reversing the motion of the piston. wherein the two rebound chambersare gaseous chambers acting as compression springs on opposite faces ofthe piston.

9. The apparatus of claim I further including a second port in thecylinder side wall. said passageway further communicating with thecylinder via said second port, wherein the two ports are located atdifferent axial positions in the cylinder side wall, and the axiallength of the by-passed cylinder portion is determined primarily by theaxial separation and size of said ports.

Ill. The apparatus ofclaim I wherein the axial length of said by-passcdcylinder portion is less than the axial length of the piston side wall.

ll. The apparatus of claim I wherein the passageway is of integralconstruction.

I2. The apparatus of claim 1 wherein said controlling means comprisesgroove means in the cylinder wall in said by-passed portion of thecylinder.

13. The apparatus of claim I wherein said passageway has no movingparts.

14. The apparatus of claim 1 wherein the controlling means has no movingparts.

15. The apparatus of claim I wherein the sustaining means has no movingparts other than the piston itself.

16. The apparatus of claim I wherein the controlling means is ofintegral construction.

17. An oscillating piston apparatus comprising two cylinders, a freepiston in each cylinder, each of said cylinders having a side wall witha port therein. means for sustaining oscillatory motion of each pistonin its cylinder, and means for controlling the locations of the centersof oscillation of the pistons in their cylinders, said controlling meansincluding: a common chamber for the two cylinders. said common chambercontaining compressible fluid and having as moving wall portions oneface of each piston, a separate rebound chamher for each piston. saidrebound chamber containing compressible fluid and having as a movingwall portion the opposite face of the piston. and a fluid passageway foreach cylinder communicating with the respective cylinder via therespective port, said passageway bypassing a portion, and only aportion, of the axial length of the cylinder, said passageway having afluid flow impedance which is substantially the same for fluid flow ineither direction through the passageway; whereby the center ofoscillation of each piston is located near the midpoint of the by-passedportion of its cylinder.

18. The apparatus of claim 17 wherein the means for sustaining includesmeans for synchronizing the oscillatory motion of the pistons.

19. The apparatus of claim 17 wherein the means for sustaining includesmeans for maintaining synchronous and opposite oscillatory motion of thepistons.

20. The apparatus of claim 17 wherein the means for sustaining includesmeans for alternately heating and cooling the fluid.

21. The apparatus of claim 17 wherein the means for sustaining includesheated passageway means for re peatedly heating the fluid in the commonchamber.

22. The apparatus of claim 17 wherein the passageway for each cylinderconsists of a passageway in said portion of the cylinder wall.

23. The apparatus of claim 17 wherein said controlling means i'or eachcylinder comprises groove means in the cylinder wall in said by-passedportion of the cylinder.

24. The apparatus of claim 17 wherein said controlling means for eachcylinder includes by-pass passageway means having no moving parts.

25. The apparatus of claim 17 wherein the free pistons are each ofsubstantially integral construction.

26. The apparatus of claim 17 wherein the crosssectional dimensions ofeach piston are substantially the same throughout substantially all ofthe piston length.

27. The apparatus of claim 17 wherein the axial length of said by-passedcylinder portion is less than the axial length of the piston side wall.

28. The apparatus otclaim [7 wherein the sustaining means has no movingparts other than the two free pistons.

29. A naturally resonant oscillatory device comprising a chambercontaining compressible fluid, said chamber having structure forming atleast one peripheral wall portion susceptible to being oscillated at anut ural resonant frequency of oscillation so as to cyclically decreaseand increase the volume of the chamber, said chamber being substantiallysealed during at least a substantial portion of the oscillation cycle,said chamber having fluid passageway means communicating with the atleast one wall portion, means for heating said fluid passageway means,means for sustaining oscillatory motion of the at least one wall portionof the chamber so as to alternately decrease and increase the volume ofthe chamber, means including the oscillatory motion of the wall portionfor repeatedly inducing a flow of cool fluid into said heated passagewaymeans; said heated passageway means being designed in accordance withthe frequency of oscillation to: (a) readily admit said cool fluid, (b)heat substantially all of said admitted fluid, (0) heat fluid in thepassageway means as the oscillating wall portion moves in a direction toincrease the volume of the chamber during said portion of the cycle, and(d) eject heated compressible fluid from the passageway means into aregion of the chamber external to the passageway means as theoscillating wall portion moves in a direction to increase the volume ofthe chamber during said portion of the cycle; said cool fluid flowinducing means further including means for cooling fluid ejected fromsaid heated passageway means, said means for sustaining including: (a)the heated fluid passageway means, (b) the flow inducing means includingthe motion of said wall portion and the means for cooling ejected fluid,(c) inertia of the structure. and (d) spring action of fluid compressedby the oscillating wall portion; wherein the energy for sustaining saidoscillation is derived primarily from said heating and said cooling;wherein a net flow of fluid is induced into the heated passageway meanswhile the volume of the chamber is decreasing during said portion of thecycle, said net flow being primarily and directly responsive to pressurevariations of the fluid in the chamber resulting primarily and directlyfrom changes in the chamber volume caused by the oscillating portion.

30. The device of claim 29 wherein said means for cooling said ejectedfluid primarily comprises cooling of the ejected fluid by cool wallsurfaces of the chamber external to said heated passageway means.

3]. The device of claim 29 wherein said heating means includes means forheating said fluid passageway means substantially independently of theinstantaneous phase of said at least one oscillating peripheral wallportion.

32. The device of claim 29 wherein said at least one oscillatingperipheral wall portion includes two periph eral wall portionsoscillating substantially in synchronism so as to, substantially withthe same phase, cyclically decrease and increase the volume of thechamber.

33. The device of claim 32 wherein each of the wall portions is a freepiston oscillating in a cylinder.

34. The device of claim 33 further including groove means for eachcylinder bypassing only a portion of the cylinder for positioning thecenter of oscillation of the free piston.

35. The device of claim 32 wherein said cooling of the ejected fluidprimarily includes cooling of the ejected fluid by cool walls of thechamber external to the heated passageway means.

36. The device of claim 35 wherein said cool walls primarily includewalls of the chamber proximate the oscillating portions and the faces ofthe oscillating portions.

37. The device of claim 32 wherein the means for heating the passagewaymeans includes means for heating the passageway means substantiallyindependently of the instantaneous phases of the oscillating wallportions.

38. The device of claim 32 wherein said wall portions communicate othwith each other and with said heated passageway means via a fluid flowconnecting means, wherein said means for sustaining oscillation includescooling of said ejected fluid by cool walls of the connecting meansproximate the oscillating portions.

39. The device of claim 29 wherein said heated passageway means includesan elongated passageway having an average length substantially greaterthan its average width.

40. The device of claim 29 wherein said chamber is substantially sealedduring substantially all of the oscillatory cycle.

41. The device of claim 29 wherein said heating means includes means forheating said passageway means substantially independently of saidnatural resonant frequency of oscillation.

42. The device of claim 29 wherein said passageway means comprises anelongated passageway having an average length and an average breadtheach of which is substantially greater than the average width of thepassageway.

43. The device of claim 29 wherein there is an increase in effectiveexposure of a cool surface to fluid in the chamber as the wall portionmoves in a direction to increase the chamber volume. whereby said meansfor cooling the ejected fluid includes cooling of the ejected fluid bysaid variably exposed cool surface.

44. The device of claim 29 wherein said heating of fluid in saidpassageway means and said cooling of ejected fluid each primarilycomprises thermal transfer between the fluid and walls of the chamber.

45. The device of claim 29 wherein the means for sustaining oscillationincludes cooling of the ejected fluid by cool wall surfaces of thechamber proximate the oscillating portion.

46. The device of claim 45 wherein said cool wall surfaces include anexposed face of the oscillating portion.

47. The device of claim 29 wherein the heated passageway means includesan elongated passageway having a characteristic passageway widthselected in accordance with the oscillatory frequency to augment saidoscillation.

48. The device of claim 29 wherein the heated passageway means includesa multiplicity of heated elongated passageways.

49. The device of claim 29 wherein the passageway means is formed tomate with an electric bulb which provides heat for heating thepassageway means.

50. The device of claim 29 wherein said inducing of cool fluid into saidheated passageway means for said heating and ejecting of said fluidtakes place primarily while said chamber volume is decreasing duringsaid portion of the cycle.

5]. The device of claim 29 wherein said inducing of cool fluid into saidheated passageway means for said heating and ejecting of said fluidtakes place substantially entirely while said chamber volume isdecreasing during said portion of the cycle.

S2. The device of claim 29 wherein said wall portion comprises a freepiston oscillating in the cylinder.

53. The device of claim 52 further including cylinder bypass means forpositioning the center of oscillation of the free piston in thecylinder.

54. The device of claim 53 wherein said bypass means bypasses only aportion of the cylinder. said center of oscillation being positionednear the mid-point of the bypassed portion.

55. The device of claim 54 wherein the bypass means includes a bypasspassageway bypassing said bypassed cylinder portion and havingsubstantially equal fluid flow impedance in either direction through thepassageway.

S6. The device of claim 55 wherein said passageway is of integralconstruction.

57. The device of claim 55 wherein said passageway is integral with thecylinder.

58. The device of claim 55 wherein said bypass means comprises groovemeans in the cylinder sidewall.

59. The device of claim 55 wherein said bypass means comprises means forforming the cylinder side wall to provide a lower impedance to fluidflow between the piston and cylinder side walls in the bypassed portionof the cylinder than in portions of the cylinder beyond the bypassedportion.

60. A naturally resonant oscillatory device comprising a variable volumechamber. said chamber having structure forming at least one wall portionsusceptible to being oscillated at a natural resonant frequency ofoscillation so as to alternately decrease and increase the volume of thechamber. said chamber maintained in a substantially closed conditionduring at least a portion of the oscillation cycle. said chamber havingfluid passageway means communicating with the at least one Wall portion.means for heating said fluid passageway means means for sustainingoscillatory motion of the at least one wall portion of the chamber so asto alternately decrease and increase said chamber volume. meansincluding the oscillatory motion of the wall portion for cyclicallyinducing a flow of cool fluid into said heated passageway means; saidheated passageway means having a geometry and an average passagewaywidth selected in accordance with the frequency of oscillation toreadily admit said cool fluid and to heat by thermal transfer meanssubstantially all of said admitted fluid so as to eject heatedcompressible fluid from the heated passageway means during said portionof the cycle as the oscillating wall portion moves in the same generaldirection as the ejected fluid and to heat fluid in the heatedpassageway means during said portion of the cycle as the oscillatingwall portion moves in the same general direction as the ejectef fluid;said means for sustaining including: the heating of the fluid by saidpassageway means. the means for heating said passageway means, said flowinducing means, inertia of the structure and spring action of fluidcompressed by the oscillating wall portion; wherein a net flow of fluidis induced into the heated passageway means while the fluid is beingcompressed toward the heated passage way means by the oscillatingportion during said portion of the cycle, said net flow being primarilyand directly responsive to pressure variations of the fluid in thechamber resulting primarily and directly from changes in the chambervolume caused by the oscillating portion.

61. The device of claim 60 wherein said cool fluid inducing meansincludes thermal transfer means for cooling said ejected fluid.

62. The device of claim 6| wherein said cooling means primarily includescooling of the ejected fluid by cool walls of the chamber external tothe heated passageway means.

63. The device of claim 6] wherein said cooling means includes coolingof the ejected fluid by cool walls of the chamber cyclically varied ineffective exposure to the fluid by the oscillating portion.

64. The device of claim 61 wherein said cooling provides the primarycooling for sustaining said oscillation.

65. The device of claim 60 wherein the cool fluid inducing meansprimarily includes cooling of the ejected fluid by cool walls of thechamber proximate the oscillating portion.

66. The device otclaim 60 wherein the cool fluid inducing means includesmeans for cooling the induced fluid.

67. The device of claim 66 wherein the energy for sustaining saidoscillation is derived primarily from said heating and said cooling.

68. The device of claim 60 wherein the heat energy for sustaining saidoscillation is provided primarily by said heating.

6). The device of claim 60 wherein said fluid passageway means is heatedsubstantially independently of the instantaneous phase of theoscillating portion.

70. The device of claim 69 wherein the at least one oscillatingperipheral wall portion includes two periph eral wall portionsoscillating substantially in synchronism so as to substantially togetheralternately decrease and increase said chamber volume.

71. The device of claim 70 wherein each of the wall portions is a freepiston oscillating in a cylinder.

72. The device of claim 7l wherein the heated passageway means is formedto be heated by an electric light bulb which provides sufficient heatenergy for sustaining said oscillation while providing light forillumination of the surroundings.

73. The device of claim 72 further including groove means in the insidesurface of the sidewall of each of said cylinders for controlling thecenter ofoscillation of each piston in its cylinder.

74. The device of claim 70 wherein said wall portions communicate bothwith each other and with said heated passageway means via a fluidconnecting means. and wherein said means for sustaining oscillation ineludes cooling of said induced fluid by cool walls of the connectingmeans proximate the oscillating portions.

75. The device of claim 69 wherein said heated passageway means includesan elongated passageway having an average length and an :ueragc breadtheach of which is substantially greater than the average width of til thepassageway.

76. The device of claim 69 wherein said chamber is substantially sealedduring substantially all of the oscillatory cycle.

77. The device of claim 69 wherein the heated passageway means includesa multiplicity of elongated heated passageways.

78. The device of claim 69 wherein said inducing of cool fluid into saidpassageway means for said heating and ejecting of said fluid takes placesubstantially en tirely while said chamber volume is decreasing duringsaid portion of the cycle.

79. The device of claim wherein said passageway means is heatedsubstantially independently of said natural resonant frequency ofoscillation.

80. The device of claim 50 wherein said ejected heated fluid is derivedprimarily from cool fluid induced into said heated passageway meanswhile said chamber volume decreases during said portion of the cycle.

8|. The device of claim 60 wherein said inducing of cool fluid into saidpassageway means for said heating and ejecting of said fluid takes placeprimarily while said chamber volume is decreasing during said portion ofthe cycle.

82. The device of claim 60 wherein the wall portion comprises a freepiston oscillating in a cylinder.

83. The device of claim 82 further including means bypassing only aportion of the cylinder to position the center of oscillation of thefree piston within the by passed portion.

84. The device of claim 83 wherein the bypass means includes a bypasspassageway bypassing said cylinder portion and having substantiallyequal impedance for fluid flow in either direction through thepassageway.

85. The device of claim 83 wherein said bypass means comprises means forforming the cylinder sidewall to provide a greater mean separationbetween the piston and cylinder side walls in the bypassed cylinderportion than in a cylinder portion beyond the bypassed portion.

86. The apparatus of claim 1 wherein said passageway and said portcomprise an enlargement of the inside diameter of the cylinder in aregion of the cylinder side-wall within said bypassed portion.

87. The apparatus of claim 17 wherein said passageway and said port foreach cylinder comprise an enlargement of the inside diameter of thecylinder in a region of the cylinder side-wall within said bypassedportion.

88. The device of claim 82 further including means bypassing only aportion of the cylinder to position the center of oscillation of thefree piston near the bypassed portion.

i l r

1. An oscillating piston apparatus comprising a cylinder, a free pistonin the cylinder, said cyliner having a side wall with a port therein, arebound chamber containing compressible fluid for reversing the motionof the piston. said rebound chamber having as a moving wall portion aface of the piston, means including said rebound chamber for sustainingoscillatory motion of the piston in the cylinder and means forcontrolling the location of the center of oscillation of the piston inthe cylinder, said controlling means including said rebound chamber anda passageway communicating with the cylinder via the port, saidpassageway bypassing a portion, and only a portion of the axial lengthof the cylinder, said passageway having a fluid flow impedance which issubstantially the same for fluid flow in either direction through thepassageway, wherein said port, said by-passed portion of the cylinder,and an unbypassed portion of the cylinder are all at least partiallytraversed by the piston.
 2. The apparatus of claim 1 wherein the freepiston is of substantially integral construction.
 3. The apparatus ofclaim 1 wherein the cross-sectional dimensions of the free piston aresubstantially the same throughout substantially all of its length. 4.The apparatus of claim 1 wherein the means for sustaining includes meansfor alternately heating and cooling the fluid.
 5. The apparatus of claim1 wherein the means for sustaining includes heated passageway meanscommunicating with said cylinder.
 6. The apparatus of claim 5 furtherincluding means for heating said heated passageway means.
 7. Theapparatus of claim 5 wherein said heated passageway means includes atleast one passageway having a characteristic length and breadth whichare each substantially greater than its characteristic width.
 8. Theapparatus of claim 1 further including another rebound chamber forreversing the motion of the piston, wherein the two rebound chambers aregaseous chambers acting as compression springs on opposite faces of thepiston.
 9. The apparatus of claim 1 further including a second port inthe cylinder side wall, said passageway further communicating with thecylinder via said second port, wherein the two ports are located atdifferent axial positions in the cylinder side wall, and the axiallength of the by-passed cylinder portion is determined primarily by theaxial separation and size of said ports.
 10. The apparatus of claim 1wherein the axial length of said by-passed cylinder portion is less thanthe axial length of the piston side wall.
 11. The apparatus of claim 1wherein the passageway is of integral construction.
 12. The apparatus ofclaim 1 wherein said controlling means comprises groove means in thecylinder wall in said by-passed portion of the cylinder.
 13. Theapparatus of claim 1 wherein said passageway has no moving parts. 14.The apparatus of claim 1 wherein the controlling means has no movingparts.
 15. The apparatus of claim 1 wherein the sustaining means has nomoving parts other than the piston itself.
 16. The apparatus of claim 1wherein the controlling means is of integral construction.
 17. Anoscillating piston apparatus comprising two cylinders, a free piston ineach cylinder, each of said cylinders having a side wall with a porttherein, means for sustaining oscillatory motion of each piston in itscylinder, and means for controlling the locations of the centers ofoscillation of the pistons in their cylinders, said controlling meansincluding: a common chamber for the two cylinders, said common chambercontaining compressible fluid and having as moving wall portions oneface of each piston, a separate rebound chamber for each piston, saidrebound chamber containing compressible fluid and having as a moviNgwall portion the opposite face of the piston, and a fluid passageway foreach cylinder communicating with the respective cylinder via therespective port, said passageway by-passing a portion, and only aportion, of the axial length of the cylinder, said passageway having afluid flow impedance which is substantially the same for fluid flow ineither direction through the passageway; whereby the center ofoscillation of each piston is located near the mid-point of theby-passed portion of its cylinder.
 18. The apparatus of claim 17 whereinthe means for sustaining includes means for synchronizing theoscillatory motion of the pistons.
 19. The apparatus of claim 17 whereinthe means for sustaining includes means for maintaining synchronous andopposite oscillatory motion of the pistons.
 20. The apparatus of claim17 wherein the means for sustaining includes means for alternatelyheating and cooling the fluid.
 21. The apparatus of claim 17 wherein themeans for sustaining includes heated passageway means for repeatedlyheating the fluid in the common chamber.
 22. The apparatus of claim 17wherein the passageway for each cylinder consists of a passageway insaid portion of the cylinder wall.
 23. The apparatus of claim 17 whereinsaid controlling means for each cylinder comprises groove means in thecylinder wall in said by-passed portion of the cylinder.
 24. Theapparatus of claim 17 wherein said controlling means for each cylinderincludes by-pass passageway means having no moving parts.
 25. Theapparatus of claim 17 wherein the free pistons are each of substantiallyintegral construction.
 26. The apparatus of claim 17 wherein thecross-sectional dimensions of each piston are substantially the samethroughout substantially all of the piston length.
 27. The apparatus ofclaim 17 wherein the axial length of said by-passed cylinder portion isless than the axial length of the piston side wall.
 28. The apparatus ofclaim 17 wherein the sustaining means has no moving parts other than thetwo free pistons.
 29. A naturally resonant oscillatory device comprisinga chamber containing compressible fluid, said chamber having structureforming at least one peripheral wall portion susceptible to beingoscillated at a natural resonant frequency of oscillation so as tocyclically decrease and increase the volume of the chamber, said chamberbeing substantially sealed during at least a substantial portion of theoscillation cycle, said chamber having fluid passageway meanscommunicating with the at least one wall portion, means for heating saidfluid passageway means, means for sustaining oscillatory motion of theat least one wall portion of the chamber so as to alternately decreaseand increase the volume of the chamber, means including the oscillatorymotion of the wall portion for repeatedly inducing a flow of cool fluidinto said heated passageway means; said heated passageway means beingdesigned in accordance with the frequency of oscillation to: (a) readilyadmit said cool fluid, (b) heat substantially all of said admittedfluid, (c) heat fluid in the passageway means as the oscillating wallportion moves in a direction to increase the volume of the chamberduring said portion of the cycle, and (d) eject heated compressiblefluid from the passageway means into a region of the chamber external tothe passageway means as the oscillating wall portion moves in adirection to increase the volume of the chamber during said portion ofthe cycle; said cool fluid flow inducing means further including meansfor cooling fluid ejected from said heated passageway means, said meansfor sustaining including: (a) the heated fluid passageway means, (b) theflow inducing means including the motion of said wall portion and themeans for cooling ejected fluid, (c) inertia of the structure, and (d)spring action of fluid compressed by the oscillating wall portion;wherein the energy for sustaining said oscillation is derived primarilyfrom said heating and saiD cooling; wherein a net flow of fluid isinduced into the heated passageway means while the volume of the chamberis decreasing during said portion of the cycle, said net flow beingprimarily and directly responsive to pressure variations of the fluid inthe chamber resulting primarily and directly from changes in the chambervolume caused by the oscillating portion.
 30. The device of claim 29wherein said means for cooling said ejected fluid primarily comprisescooling of the ejected fluid by cool wall surfaces of the chamberexternal to said heated passageway means.
 31. The device of claim 29wherein said heating means includes means for heating said fluidpassageway means substantially independently of the instantaneous phaseof said at least one oscillating peripheral wall portion.
 32. The deviceof claim 29 wherein said at least one oscillating peripheral wallportion includes two peripheral wall portions oscillating substantiallyin synchronism so as to, substantially with the same phase, cyclicallydecrease and increase the volume of the chamber.
 33. The device of claim32 wherein each of the wall portions is a free piston oscillating in acylinder.
 34. The device of claim 33 further including groove means foreach cylinder bypassing only a portion of the cylinder for positioningthe center of oscillation of the free piston.
 35. The device of claim 32wherein said cooling of the ejected fluid primarily includes cooling ofthe ejected fluid by cool walls of the chamber external to the heatedpassageway means.
 36. The device of claim 35 wherein said cool wallsprimarily include walls of the chamber proximate the oscillatingportions and the faces of the oscillating portions.
 37. The device ofclaim 32 wherein the means for heating the passageway means includesmeans for heating the passageway means substantially independently ofthe instantaneous phases of the oscillating wall portions.
 38. Thedevice of claim 32 wherein said wall portions communicate both with eachother and with said heated passageway means via a fluid flow connectingmeans, wherein said means for sustaining oscillation includes cooling ofsaid ejected fluid by cool walls of the connecting means proximate theoscillating portions.
 39. The device of claim 29 wherein said heatedpassageway means includes an elongated passageway having an averagelength substantially greater than its average width.
 40. The device ofclaim 29 wherein said chamber is substantially sealed duringsubstantially all of the oscillatory cycle.
 41. The device of claim 29wherein said heating means includes means for heating said passagewaymeans substantially independently of said natural resonant frequency ofoscillation.
 42. The device of claim 29 wherein said passageway meanscomprises an elongated passageway having an average length and anaverage breadth each of which is substantially greater than the averagewidth of the passageway.
 43. The device of claim 29 wherein there is anincrease in effective exposure of a cool surface to fluid in the chamberas the wall portion moves in a direction to increase the chamber volume,whereby said means for cooling the ejected fluid includes cooling of theejected fluid by said variably exposed cool surface.
 44. The device ofclaim 29 wherein said heating of fluid in said passageway means and saidcooling of ejected fluid each primarily comprises thermal transferbetween the fluid and walls of the chamber.
 45. The device of claim 29wherein the means for sustaining oscillation includes cooling of theejected fluid by cool wall surfaces of the chamber proximate theoscillating portion.
 46. The device of claim 45 wherein said cool wallsurfaces include an exposed face of the oscillating portion.
 47. Thedevice of claim 29 wherein the heated passageway means includes anelongated passageway having a characteristic passageway width selectedin accordance with the oscillatory frequency to augment saidoscillation.
 48. The device of clAim 29 wherein the heated passagewaymeans includes a multiplicity of heated elongated passageways.
 49. Thedevice of claim 29 wherein the passageway means is formed to mate withan electric bulb which provides heat for heating the passageway means.50. The device of claim 29 wherein said inducing of cool fluid into saidheated passageway means for said heating and ejecting of said fluidtakes place primarily while said chamber volume is decreasing duringsaid portion of the cycle.
 51. The device of claim 29 wherein saidinducing of cool fluid into said heated passageway means for saidheating and ejecting of said fluid takes place substantially entirelywhile said chamber volume is decreasing during said portion of thecycle.
 52. The device of claim 29 wherein said wall portion comprises afree piston oscillating in the cylinder.
 53. The device of claim 52further including cylinder bypass means for positioning the center ofoscillation of the free piston in the cylinder.
 54. The device of claim53 wherein said bypass means bypasses only a portion of the cylinder,said center of oscillation being positioned near the mid-point of thebypassed portion.
 55. The device of claim 54 wherein the bypass meansincludes a bypass passageway bypassing said bypassed cylinder portionand having substantially equal fluid flow impedance in either directionthrough the passageway.
 56. The device of claim 55 wherein saidpassageway is of integral construction.
 57. The device of claim 55wherein said passageway is integral with the cylinder.
 58. The device ofclaim 55 wherein said bypass means comprises groove means in thecylinder side-wall.
 59. The device of claim 55 wherein said bypass meanscomprises means for forming the cylinder side wall to provide a lowerimpedance to fluid flow between the piston and cylinder side walls inthe bypassed portion of the cylinder than in portions of the cylinderbeyond the bypassed portion.
 60. A naturally resonant oscillatory devicecomprising a variable volume chamber, said chamber having structureforming at least one wall portion susceptible to being oscillated at anatural resonant frequency of oscillation so as to alternately decreaseand increase the volume of the chamber, said chamber maintained in asubstantially closed condition during at least a portion of theoscillation cycle, said chamber having fluid passageway meanscommunicating with the at least one wall portion, means for heating saidfluid passageway means, means for sustaining oscillatory motion of theat least one wall portion of the chamber so as to alternately decreaseand increase said chamber volume, means including the oscillatory motionof the wall portion for cyclically inducing a flow of cool fluid intosaid heated passageway means; said heated passageway means having ageometry and an average passageway width selected in accordance with thefrequency of oscillation to readily admit said cool fluid and to heat bythermal transfer means substantially all of said admitted fluid so as toeject heated compressible fluid from the heated passageway means duringsaid portion of the cycle as the oscillating wall portion moves in thesame general direction as the ejected fluid and to heat fluid in theheated passageway means during said portion of the cycle as theoscillating wall portion moves in the same general direction as theejectef fluid; said means for sustaining including: the heating of thefluid by said passageway means, the means for heating said passagewaymeans, said flow inducing means, inertia of the structure and springaction of fluid compressed by the oscillating wall portion; wherein anet flow of fluid is induced into the heated passageway means while thefluid is being compressed toward the heated passageway means by theoscillating portion during said portion of the cycle, said net flowbeing primarily and directly responsive to pressure variations of thefluid in the chamber resulting primarily and directly from changes intHe chamber volume caused by the oscillating portion.
 61. The device ofclaim 60 wherein said cool fluid inducing means includes thermaltransfer means for cooling said ejected fluid.
 62. The device of claim61 wherein said cooling means primarily includes cooling of the ejectedfluid by cool walls of the chamber external to the heated passagewaymeans.
 63. The device of claim 61 wherein said cooling means includescooling of the ejected fluid by cool walls of the chamber cyclicallyvaried in effective exposure to the fluid by the oscillating portion.64. The device of claim 61 wherein said cooling provides the primarycooling for sustaining said oscillation.
 65. The device of claim 60wherein the cool fluid inducing means primarily includes cooling of theejected fluid by cool walls of the chamber proximate the oscillatingportion.
 66. The device of claim 60 wherein the cool fluid inducingmeans includes means for cooling the induced fluid.
 67. The device ofclaim 66 wherein the energy for sustaining said oscillation is derivedprimarily from said heating and said cooling.
 68. The device of claim 60wherein the heat energy for sustaining said oscillation is providedprimarily by said heating.
 69. The device of claim 60 wherein said fluidpassageway means is heated substantially independently of theinstantaneous phase of the oscillating portion.
 70. The device of claim69 wherein the at least one oscillating peripheral wall portion includestwo peripheral wall portions oscillating substantially in synchronism soas to substantially together alternately decrease and increase saidchamber volume.
 71. The device of claim 70 wherein each of the wallportions is a free piston oscillating in a cylinder.
 72. The device ofclaim 71 wherein the heated passageway means is formed to be heated byan electric light bulb which provides sufficient heat energy forsustaining said oscillation while providing light for illumination ofthe surroundings.
 73. The device of claim 72 further including groovemeans in the inside surface of the side-wall of each of said cylindersfor controlling the center of oscillation of each piston in itscylinder.
 74. The device of claim 70 wherein said wall portionscommunicate both with each other and with said heated passageway meansvia a fluid connecting means, and wherein said means for sustainingoscillation includes cooling of said induced fluid by cool walls of theconnecting means proximate the oscillating portions.
 75. The device ofclaim 69 wherein said heated passageway means includes an elongatedpassageway having an average length and an average breadth each of whichis substantially greater than the average width of the passageway. 76.The device of claim 69 wherein said chamber is substantially sealedduring substantially all of the oscillatory cycle.
 77. The device ofclaim 69 wherein the heated passageway means includes a multiplicity ofelongated heated passageways.
 78. The device of claim 69 wherein saidinducing of cool fluid into said passageway means for said heating andejecting of said fluid takes place substantially entirely while saidchamber volume is decreasing during said portion of the cycle.
 79. Thedevice of claim 60 wherein said passageway means is heated substantiallyindependently of said natural resonant frequency of oscillation.
 80. Thedevice of claim 50 wherein said ejected heated fluid is derivedprimarily from cool fluid induced into said heated passageway meanswhile said chamber volume decreases during said portion of the cycle.81. The device of claim 60 wherein said inducing of cool fluid into saidpassageway means for said heating and ejecting of said fluid takes placeprimarily while said chamber volume is decreasing during said portion ofthe cycle.
 82. The device of claim 60 wherein the wall portion comprisesa free piston oscillating in a cylinder.
 83. The device of claim 82further including means bypassing only a portion of the cylinder toPosition the center of oscillation of the free piston within thebypassed portion.
 84. The device of claim 83 wherein the bypass meansincludes a bypass passageway bypassing said cylinder portion and havingsubstantially equal impedance for fluid flow in either direction throughthe passageway.
 85. The device of claim 83 wherein said bypass meanscomprises means for forming the cylinder side-wall to provide a greatermean separation between the piston and cylinder side walls in thebypassed cylinder portion than in a cylinder portion beyond the bypassedportion.
 86. The apparatus of claim 1 wherein said passageway and saidport comprise an enlargement of the inside diameter of the cylinder in aregion of the cylinder side-wall within said bypassed portion.
 87. Theapparatus of claim 17 wherein said passageway and said port for eachcylinder comprise an enlargement of the inside diameter of the cylinderin a region of the cylinder side-wall within said bypassed portion. 88.The device of claim 82 further including means bypassing only a portionof the cylinder to position the center of oscillation of the free pistonnear the bypassed portion.